I checked my tube sub guide, produced by Sams, and I think they really goofed. They list subs for the 5BK7A as 4BC8, 4BQ7A, 4BS8, 4BX8, 4BZ7 and 4BZ8.

I'm sure these are supposed to be 5 volt tubes, so the 5BQ7A should be OK.

Actually the GE tube manual shows a difference in filament current, so the 5BQ7 is not a good sub for the 5BK7 according to their data, but the 4 volt tubes listed above apparently would be. I would have expected the 5 volt subs to be the correct ones......

Either way, that 5BQ7 checked bad in my checker, so I have a new 5BK7 on the way.

The new tuner tube came into day. I've got a good sharp pic but no vertical or horiz sync. I've still got 4 electrolytics to replace, so until I get them changed out, I'm not going to do any maj troubleshooting. I did check the voltages on the sync tube, and they are correct.
Doug

Now I need some help. The rest of my filters came in today. I put them in except for C1 (which checked excellent on my checker), and I still have no horiz or vertical sync.
Voltages on the sync tube 3CS6 (V9) are normal. Voltages are normal on Video IF tubes are normal also. The only paper cap I have not replaced is C71 coming off the 3AL5 Horizontal AFC tube. Any ideas on where to go next?

Thanks
Doug

Looks like a nice purchase. I don't have access at the moment to a Sams 373, but it appeared to me from one of your photos that you had some semblance of horizontal & vertical sync before you changed the 5BQ7.

Bluestar1, with the old 5BQ7 in the set (that was in there when I got it) I mainly get snow. The tube checks bad in my checker. Sometimes I can get a snowy pic. I just put that tube back in again and tried it. I was able to get a very snowy pic but could sync the horiz. It almost had to be maxed out to sync though. After playing with the height and lin controls, I was finally able to syn the vert, but it was so snowy that I could tell if the pic was linear.

Replacing that bad tuner tube with the correct new one does give a sharp pic but no sync. I also just replaced that last paper cap C71, but no improvement. I had the same problem on a metal cabinet Admiral I did recently, and someone posted that perhaps my pic was overloaded.
Doug

Overloaded picture and no sync are two separate things. Have you lost both vertical and horizontal sync?

Johnnysan, yes I have no horis or vert sync as in the pic below. The reasons I was thinking about overloaded pic was 1: I've got it on cable, and the local/distant switch has NO effect. I've never had a set where moving that switch doesn't have some effect.
2. One part of that switch goes thru a 1.5m resistor (which I replaced) and onto pin 7 of the 3CS6 (sync sep) tube.

Your problem is around the 3CS6 sync separator. Did you re-cap this circuit? There is a goofy couplet-looking resistor that is 90k with a shield; it goes to the vertical circuit so it may not be your whole problem. Make sure your 255 volts B+ is normal. If you have a scope test the grid 1 and plate waveforms.

Yes, I have recapped this circut. To be honest, last night I found I had missed a paper cap(C61) going to pin 7 of the 3CS6. Hoping that was my problem, I replaced it, but no improvement. This morning I did replace the mica cap C60 (470) as well as several resistors: R54, and R65. I have not replace R66 yet which is the 390K coming off the 255 B+ then going to pin 5. My 255V is normal, reading about 260V. Voltages on the 3CS6 are normal too.

On that 90K shielded resistor you mentioned, I wonder if it would be possible to make one for a sub?

Doug

Johnnysan, I understand where you're coming from about overloaded pic and sync being 2 different issues. I want to show you two pics, each one with the contrast at each extreme. I got the horis to be somewhat stable long enough to snap this pic. At min contrast, it seems like there is too much. The words at the bottom of the CNN screen seem too distorted. At max contrast, it's so bad I can't get the pic to stabalize at all.

Did you replace C47, which is on the contrast control? And C61, which is at pin 1 on the 3CS6?

C61 was replaced last night. C47 was replaced earlier. I checked the rest of the resistors in the contrast circut and replaced R55 (220K). Also replaced R66 (390K) off pin 5 in the sync cirut. Still no improvement.
Doug

Did you install a new 3CS6 tube? After that, I recommend double checking the parts that have been replaced.

Well I don't know what happened. I was behind the set and had made some voltage checks on some of the tubes, and I look around at the screen, and I had perfect sync. It payed from 9:45 til 11:15 tonight and didn't lose sync once. I'll fire it up tomorrow and see what happens. I did notice that the audio now has more buzz in it than when I first started working on it. I can get most of it out by the fine tuning and buzz control, but not all of it.

Doug

Perhaps some speck of gunk or corrosion in a socket or control finally gave way, and now <whatever> made contact again. Or perhaps you have an intermittent that is making contact again for the moment.

If this was a very dirty set, it might pay to go back and re-clean all of the tube pins and sockets, and all controls & switches. Sometimes a little spritz is not enough.

Phil Nelson

Well my success was short lived. I turned it on Sun, and it played fine. However the audio buzz got louder, and I couldn't get it all adjusted with the buzz control. I took out that new 5BK7, in the tuner, and put the sub 4BS8 back in. When I turned it on, I had lost sync again. I pulled the tube and sprayed Deoxit in that tuner tube socket. I put the new 5BK7 back in, and still had no sync. However after playing for 10 min, the sync cleared up. It played fine for over an hr.
This morning I had no sync again. It's played for over 30 min and has not cleared up. I got back into the chasis and replaced a disc and mica cap in the hioirz mult section. C76 (330mmf) and C68 (68mmf) but no improvement.

Doug

This is why an oscilloscope is essential for TV work.

I've got one, but it doesn't work. I bought one off ebay last yr which was supposed to work. While waiting for it, I downloaded a manual for it. When it arrived, the vertical gain control was missing. There's just a hold in the front panel where the control was. It will power up though. I was so disgusted with it that I just set it aside. One day I will open it up and see about replacing the control.